INDUSTRIAL A N D ENGIiZ'EERING CHEMISII'R Y
852
maxima a t 84.5 per cent and 100 per cent sulfuric acid, corresponding to the compositions of the compounds H2S04.H2O and H2S04, respectively, and a minimum a t 94.5 per cent sulfuric acid. The viscosities found by the authors are, however, very much lower than those found by Dunstan and Wilson for mixtures of the same composition. For example, according to the authors the mixture containing 84.5 per cent sulfuric has an absolute viscosity of 20 centipoises, while Dunstan and Wilson give, for the same mixture, a viscosity of 94 centipoises. The results for the viscosities at 25" C. agree substantially with the results obtained by Wagner at this same temperature. It will be observed that the maxima and the minimum are much less pronounced a t 75" C. than at the lower temperatures, which seems to indicate that the hydrate complexes to which the viscosity of the more concentrated solutions is due are largely dissociated a t the higher temperature. This
Vol. 15, KO.8
hypothesis is supported by the fact that the rate of decrease of viscosity with increasing temperature is very much greater with the concentrated solutions than with the dilute solutions, owing to the superimposed effects of two factors-the normal increase in fluidity, and the increasing dissociation of the hydrate complexes. These changes in viscosity with the temperatures are plotted in Fig. 5 . The results obtained for the viscosities of mixtures of sulfuric acid and water are not only of general scientific interest, but are also of value in calculating the rates of flow of such mixtures through pipes, using the modified Fanning formula given by Wilson, McAdams, and Seltzer.6 They have also a very direct application in the explanation of the effect of temperature upon the performance of the lead storage cell. Further work on the viscosity of fuming sulfuric acid is in progress. 6
THISJOURNAL, 14, 105 (1922).
Tungsten Wire for Hydrogen -Ion Determinations' By John R. Baylis BALTIMORE CITY WATERDEPARTMENT, BALTIMORE, MD.
H
YDROGEK-ION tests are now regarded as a necessity in an increasing number of industries, due to its
ences due to the constituents of the solution are not serious so long as the substance being added, or being changed, will produce differences that are readily measurable and indicative of certain reactions. With the hope of developing an electrode that does not require the use of a gas and that may be used to indicate pH changes produced by the application of chemicals for purifying Baltimore's water supply, the author has tried several metals in connection with the mercury-calomel half-cell. It was found that the tungsten wire in an ordinary 40-watt electric lamp gives such uniform results within certain p H ranges as to be suggestive of being useful for such work. The maximum range of the water since the tests were started three months previous to this writing has been pH from 6.5 to 8.6. The useful range may not extend greatly beyond these figures, but this covers a very important range. There is a voltage difference of approximately 0.09 for each
giving indication of certain stages of chemical reactions. This is leading to the demand for instruments that will automatically record the pH changes. While the hydrogen electrode gives an accurate measurement of the hydrogenion concentration of inany solutions, the method of making such determinations and the care necessary for accurate results make it difficult to construct a machine that will constantly indicate the pH. If the use of hydrogen gas could be eliminated, one I' e r y troublesome element would be reTO POTENTIOMETER moved. Y
FIG. TUNGSTEN LAMPELECTRODE Most efforts heretofore have been to develop an electrode that will give the hydrogen-ion concentration of most any solution by producing the same voltages-that is, an electrode where 0.8 volt will mean the same concentration for any solution regardless of its nature. This would be the ideal electrode, but such exacting demands are not necessary for many uses. Assuming the ideal to be impractical, the next best thing is one t h a t will give voltage differences that are indicative of pH changes in the solution. If 0.4 volt in one solution indicates a DH of 7.0 and 0.8 volt in another indicates the same pH, tGere should be no great difficultyin applying such conditions to the industries, provided pH changes produce voltages that are readily measurable. If a certain solution gives a voltage of 0.3 a t a temperature of 10" C. and 0.4 a t a temperature of 30" C., this is not serious so long as the temperature effect is known. Voltage differI
Received May 5 , 1923
0.400
1
0.350
v)
40
0.300
> 0.250
' o.200
0*'50 6.0
6.5
7.0
7.5
8.0
8.5
